LU-8191 ptlrpc: convert functions to static

LU-8191 ptlrpc: convert functions to static

Static analysis shows that a number of functions
could be made static. This patch declares several
functions in ptlrpc static.

Lustre-change: https://review.whamcloud.com/51353
Lustre-commit: 41d94aa9c9c01fa88ae152625d5ffd97256bab73

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: If0d92f7f4e625c146833f360806ae80b8914cc20
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54601
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>